Vertical seismic profiling (commonly abbreviated to the shorter name VSP) is one of the rapidly developing areas of geophysical technology in the Western hemisphere. The measurement basically involves recording the total upgoing and downgoing seismic wavefields propagating through a stratigraphic section by means of geophones clamped to the wall of a drilled well. In most seismic measurements, both the energy source and the receivers are positioned on the earth's surface. What happens to the seismic wavelet as it propagates from the source to a subsurface reflector and back to the receivers is mostly a matter of inference based on the characteristics of the source and on the properties of the wavefield measured at the surface. Vertical seismic profiling replaces much of t is inference with several closely-spaced direct physical measurements of the seismic wavefield in the real earth conditions that exist between the earth's surface and the subsurface reflector. These measurements are proving to be invaluable in structural, stratigraphic, and lithological interpretations of the subsurface and are particularly valuable when combined with surface-recorded seismic data covering a prospective area around a VSP well.

VSP wavefield measurements provide two vital pieces of information needed in seismic stratigraphy: (1) they calibrate seismic signals in terms of the geology that exists at the depths where upgoing reflections are created; and (2) they provide an additional, and usually an improved, image of subsurface geology near a VSP well. Several examples of VSP data will be shown and discussed in order to illustrate how vertical seismic profiling accomplishes these two objectives of seismic calibration and geological imaging.